Greenhouses, growth chambers, grow boxes and other indoor enclosures (hereinafter collectively referred to as “plant enclosures”) provide controlled environments designed to protect germinating seedlings, bulbs, cuttings, or young plants from harsh weather that might otherwise be detrimental to their growth. More than offer protection, such plant enclosures include certain features that allow for optimum plant growth.
A greenhouse is a building made from glass or is a tunnel-shaped structure made from plastic. It houses numerous plants that are typically arranged in an array (i.e., along rows and columns). Above this arrangement, many light sources are suspended such that the light emanating from them is distributed to the plants below. Light incident on these plants provides them with the requisite energy to promote photosynthesis, which is necessary for plant growth. Modern greenhouses also allow other features such as automatic temperature control, ventilation and semi-automatic watering and feeding to optimize plant growth.
In a grow box, one or a few germinating seeds and grow seedlings that are sensitive to harsh environments such as short days, freezing or dry air are grown. As a result, grow boxes may not be as elaborate as modern greenhouses. However, they at a minimum include a single light source to foster plant growth.
A growth chamber provides a more accurately controlled environment than a greenhouse or a grow box and is typically used for research purposes. It may be used in other cases where it is important to have known repeatable environmental factors to grow plants. Typically, young plants, which tend to be sensitive to their environment, are well suited to be grown in growth chambers.
Use of artificial light in plant enclosures has increased over the years for various reasons. These include the need for year round production of small potted flowering plants, exotic flowers, fresh fruits, vegetables, herbs, growth of plant cuttings, bulbs, seeds and other propagules, and early start of bedding plants. In greenhouses supplemental lighting is essential to maintain constant day-lengths, as for example 14 or 16 hours, throughout the year, and to supplement sunlight in order to boost photosynthetic activity where sunlight intensity is low, as for example in northern climates and foggy areas. In growth chambers, grow boxes, and indoor spaces all of the light for plant growth is provided by artificial conventional lighting. This has produced a strong practical interest in the field of artificially illuminating vegetation.
Unfortunately, the use of conventional lamps, including fluorescent lamps, high pressure sodium lamps, and metal halide lamps for artificial illumination during plant growth suffers from a number of drawbacks. By way of example, artificial illumination by conventional lamps result in undesired slow rate of total plant growth or biomass production, low final dry and wet weights of the plants, small numbers and sizes of flowers, fruits, and seeds. Furthermore the plants may be excessively “leggy,” that is elongated and spindly so that they may not stand erect, or they do not have the compact appearance demanded by the market.
As another example, the operating expenses of grow lamps used in conventional greenhouses and growth chambers can also be significant because they are not energy efficient. Furthermore, the operating expenses of artificial lighting for plant growth is generally excessive because the light spectra of conventional lamps are not optimized for plant photosynthesis. The largest non-labor cost in the greenhouse production of flowering potted plants, bedding plants, cut flowers and vegetables, especially in costal and northern growing regions is electrical power for supplemental lighting. By way of example, in one of the several greenhouse operations in California where more than 6000 high pressure sodium lamps ranging from about 400 watts to about 1000 watts are used, the electric bill exceeds $1,000,000 per year.
As yet another example, a significant amount of the energy produced by the light sources and ballasts, used in conventional greenhouses, is needlessly converted to large amounts of heat. To circumvent undesirable overheating inside the greenhouse, additional equipment in the greenhouse is installed to allow for frequent ventilation. The ventilation equipment represents capital costs for the greenhouse nursery and operating the equipment adds to the operating expense of the greenhouse. As a result, light sources used in conventional greenhouses add to its capital cost and operating expenses.
Therefore, what are needed are light sources, which do not encounter the drawbacks encountered by conventional light sources, such as energy inefficiency and insufficient plant biomass production.